I have never had to wait more than about 10 mins in the security queue at T4.

Note that the priority queue is not necessarily faster and is not completely separate from the general queue. It just allows you to enter the queue at the point it has reached at the top of the escalator. So when it is very busy you may be entering the queue at the halfway point. But in practice, the people entering from the priority queue tend to turn hard left and use the right hand side machines, while the people entering from the non-priority queue swarm to the left machines.

You don't want the queue on the extreme right - that's the one for those with SSSSS on their boarding passes! And this trip I did not get on secondary screening experience. So I am either looking less threatening or did something in the booking process to appear less suspicious.